Corbett said the agency expects 30,000 employees to retire during fiscal year 2010, which ends Sept. 30, 2010. More positions will be eliminated as other employees resign and those positions are not filled.

"We expect that we will be able to get to the right staffing levels through natural attrition," he told CNNMoney.com.

The USPS, which is not permitted to lay off employees, is currently under a nationwide hiring freeze. It has eliminated jobs in the past by offering early retirement packages and through attrition. It cut a whopping 40,000 positions this way in fiscal 2009 alone.

The USPS has shed more than 100,000 jobs in the last five years. It currently has about 600,000 full-time employees, down from about 705,000 full-time workers in fiscal year 2005.

The agency has seen the volume of mail that it processes plummet in recent years, crushing revenue.

Mail volume dropped by 25 billion pieces in fiscal year 2009, an "unprecedented" 13% decline compared to the year before, according to the USPS. In the same time period, operating revenues dropped 9.1% to $68.1 billion.